The present invention relates to a conveyor for sewing machines for closing the tip of hoses or the like, having high-versatility use.
It is known that hoses are generally produced with an open tip and are then subjected to a stitching or looping operation for closing the tip.
Sewing machines for performing this operation are generally constituted by a sewing unit which is fed with the hoses by means of an adapted conveyor. The conveyor is usually constituted by a pair of flat strips which are substantially co-planar, are arranged side by side and have, on their mutually facing sides, two protruding ridges which laterally delimit a passage for a portion of the hose proximate to the tip.
The conveyor is meant to arrange the hoses correctly with respect to the sewing unit, so as to achieve fully satisfactory tip closure.
Through the years, particular refinements have been devised to achieve an increasingly accurate sewing of the tip of hoses which can be compared, in terms of quality, to tip closure formed by looping.
One of these refinements consists in performing, at the end of the knitting of the hose, i.e., at the tip which remains open, a few additional rows with a particularly fine thread, such as helanca, and then some further rows with a thicker thread so as to obtain, at the end of the knitting process, a border which is thicker than the additional helanca rows.
In practice, at the end of the knitting of the hose, proximate to the tip of the hose there is a thinner portion which lies between the final border and the remaining part of the hose, both of which are thicker. This thinner portion is used to correctly position the hose, during its advancement along the conveyor, with respect to the sewing unit.
The ridges that protrude on the mutually facing sides of the two flat strips have an initial portion and a final portion which are substantially parallel and are mutually spaced in the direction of the thickness of the two flat strips. The initial portion and the final portion are joined by an inclined intermediate portion. Furthermore, above the pair of flat strips there are advancement means which engage the portion of the hose that protrudes upwards from the two flat strips so as to convey the hose along the flat strips toward the sewing unit.
In practice, the hose is inserted, with its thinner portion, between the two ridges of the two flat strips that delimit said passage, so that the final border of the hose protrudes upwards from the flat strips to be gripped by the advancement means and so that the remaining part of the hose is arranged below the ridges.
In this manner, during the advancement of the hose along the passage formed between the two flat strips, the lower border of the thinner portion of the hose, i.e., the beginning of the actual hose, is pulled, due to the combined action of the advancement means and of the intermediate inclined portion, against the lower side of the two ridges and is thus positioned correctly with respect to the sewing unit.
Despite these refinements, in some cases the tip closure performed with sewing machines of this kind can turn out to be scarcely accurate.
Particularly in its initial region, the thicker border that protrudes above the two flat strips and is meant to be taken up by the advancement means can in fact be stretched downwards toward the flat strips, causing the advancement means to grip it imperfectly and thus causing a less than satisfactory arrangement of the hose with respect to the two flat strips.
Furthermore, depending on the machines used for production and on the type of hose, it is possible to have mutually different heights for the thinner portions of the hose.
Owing to this fact, in order to achieve correct arrangement of the hoses upstream of the sewing unit it is necessary to use flat strips of different thicknesses which correspond to the different heights of the thinner portion of the hose.
The need to replace the flat strips according to the height of the thinner portion of the hoses is a problem both in terms of costs, since it is necessary to provide a plurality of flat strips, and in terms of machine productivity, since replacing the flat strips necessarily entails stopping the production of the machine.